New cancel commands: cancelunfunded, cancelhalffunded, cancelbuys, cancelsells

The first two use the regular HTTP API lib mtgoxhmac, and the last two
use the socket.  Socket seems faster but theres no real feedback in the
program. Will continue to migrate things over to the socket eventually.
Considering branching the project and maintaining 2 versions, 1
exclusively HTTP and 1 mostly socket with HTTP fallback.